Drilling motors have evolved into two main types for use down hole in the well drilling industry. The prevailing types are turbodrills and progressing cavity positive displacement motors. The progressive cavity motor is an apparatus in which a rotor with a spiral configuration rotates within a stator which has a bore section with one more radial cavity than the number of lobes on the rotor. The rotor rotates in one direction while its centerline progresses about a circular path in the opposite direction. The circular path may have a diameter only a fraction of the diameter of the rotor.
The drilling apparatus called a down hole motor is actually a motor, usually fluid powered, that is connected internally to an overall motor output shaft. The output shaft, common to most drilling motors, has to be especially ruggedized for well drilling. The output shaft, its housing and related bearings and seals, represent a composite machine that is driven by the motor and, in turn, drives a drilling head. Connecting the motor to the composite machine to form a reliable drilling apparatus comprises what has become known as a down hole motor. The motor connection to the output shaft has been a challenge, especially in the Moyno type apparatus.
Electric motors and turbodrills can be connected to the composite output machine directly unless the housing is bent to deflect the progressing well bore. Such motors can usually function with one flex unit whereas the moyno device usually requires two, axially separated, flex units.
Progressing cavity positive displacement motors usually have to be connected to the composite output machine by some form of flexing arrangement to allow the rotor centerline to traverse the circular path. When progressing cavity positive displacement drilling motors were first introduced they had two automotive type universal joints in the drive train between motor and output shaft. That arrangement had its limitations because available radial dimension did not allow large universal joints to be used, and the flex joints were often overloaded with a resultant short life.
To cope with the need for more torque to be carried by the flexing shaft, various alternatives have been tried with varied results. U.S. Pat. No. 5,205,789 issued Apr. 27, 1993 was successful but hard to continually lubricate. It also had highly stressed contact areas. High torque loads and long bit runs reduced the reliability of that design.
To assure lubrication of the flexing joints, rubber sleeves were used with mixed results. As long as they remained intact, they worked but the highly stressed contact points were still a life limiting factor. The rubber sleeves also were subject to occasional puncture which brought on early failure. Because tripping a drill string to change the down hole assembly is so costly, drilling motors need to be very reliable. Eliminating the rubber sleeve and the high stress contact points is a practical approach to improvement.
It is therefore an object of this invention to provide flexible couplers that have lubricant confined by rigid shell structures.
It is also an object of this invention to provide machine elements that eliminate the highly stressed contact areas where torque is conveyed between cooperating flex members by sliding contact.
These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of this specification, including the attached claims and appended drawings.